Many strains of Streptococcus thermophilus synthesize extracellular polysaccharides (EPS). These molecules may be produced as capsules that are tightly associated with the cell, or they may be liberated into the medium as a loose slime (i.e., “ropy” polysaccharide). Although the presence of exopolysaccharide does not confer any obvious advantage to growth or survival of S. thermophilus in milk, in situ production by this species or other dairy lactic acid bacteria typically imparts a desirable “ropy” or viscous texture to fermented milk products. Work has also shown that exopolysaccharide-producing S. thermophilus can enhance the functional properties of Mozzarella cheese. For further details see the review article of Broadbent et al. (J. dairy Sci. 86:407-423).
WO2004/085607A2 (Rhodia Chimie) describes a Streptococcus thermophilus (ST) strain comprising some specific concrete genes (termed “eps” genes) involved in the biosynthesis of EPS.
Hassan et al. (2003; J. dairy Sci. 86:1632-1638) describes 2 “Ropy” strains of Streptococcus thermophilus, CHCC3534 and CHCC3541. Both of these strains are sensitive to phages.